Problems with radioisotope dating
There are situations where it potentially fails -- for example, in cave deposits.In this situation, the cave contents are younger than both the bedrock below the cave and the suspended roof above.The simplest situation for a geologist is a "layer cake" succession of sedimentary or extrusive igneous rock units arranged in nearly horizontal layers.In such a situation, the "principle of superposition" is easily applied, and the strata towards the bottom are older, those towards the top are younger.Geochronologists do not claim that radiometric dating is foolproof (no scientific method is), but it does work reliably for most samples.
Cave deposits also often have distinctive structures of their own (e.g., spelothems like stalactites and stalagmites), so it is not likely that someone could mistake them for a successional sequence of rock units. Each of them is a testable hypothesis about the relationships between rock units and their characteristics.
It can't float in mid-air, particularly if the material involved is sand, mud, or molten rock.
The principle of superposition therefore has a clear implication for the age of a vertical succession of strata.
These are often characterised as the norm, rather than the exception.
I thought it would be useful to present an example where the geology is simple, and unsurprisingly, the method does work well, to show the quality of data that would have to be invalidated before a major revision of the geologic time scale could be accepted by conventional scientists.